1. Field of the Invention
The present invention relates to a method for manufacturing a magnetic recording medium and to a magnetic recording medium.
2. Description of the Related Arts
In the field of magnetic recording media such as hard discs, the surface recording density has been increased remarkably by various technical improvements, for example, by making magnetic particles, which constitute the recording layer, finer, changing materials to more effective ones, sophisticating the head processing, and so on, and further improvement of the surface recording density is still expected.
However, the improvement of the surface recording density by such conventional methods as making magnetic particles finer has already reached the limit. A discrete type magnetic recording medium is now proposed as a novel magnetic recording medium expected to be capable of further improving the surface recording density. The discrete type magnetic recording medium is produced by dividing a continuous recording layer into a number of divided recording elements, and filling the gaps between these divided recording elements with a non-magnetic material (see Japanese Patent Laid-Open Publication No. Hei 9-97419, for example).
An example of processing techniques capable of achieving minute division of a continuous recording layer is a dry etching process, such as a reactive ion etching process in which CO (carbon monoxide) gas with a nitrogen based compound gas such as NH3 (ammonia) gas added is used as the reactive gas (see Japanese Patent Laid-Open Publication No. H 12-322710, for example). More specifically, a mask layer is formed in a predetermined pattern on the surface of a continuous recording layer, removing the part of the continuous recording layer exposed from the mask layer by the aforementioned dry etching process using CO gas and so on as a reactive gas, and thereby dividing the continuous recording layer into a number of divided recording elements.
The mask layer left on the divided recording elements can be removed by a reactive ion etching process or the like using a chemically active gas as a reactive gas. The chemically active gas may be a gas commonly used in the field of semiconductor manufacturing, for example, fluorine-based gas such as SF6 (sulfur hexafluoride), CF4 (carbon tetrafluoride), NF3 (nitrogen trifluoride), or CHF3 (fluoroform), and chlorine-based gas such as Cl2 (chlorine), BCl3 (boron trichloride), or CHCl3 (chloroform).
In order to achieve stable flying of head, it is preferable to process and flatten the surfaces of a non-magnetic material and divided recording elements so that the surface roughness is limited to a certain degree. Processing techniques used in the field of semiconductor manufacturing, such as wet-process CMP (Chemical Mechanical Polishing) may be used for such flattening processing.
However, when the mask layer is removed from the divided recording elements using a reactive gas with strong chemical activity such as SF6 or CF4, a region around the top face and side face of the divided recording elements is apt to be subjected to deterioration such as oxidation, corrosion, or the like.
Also when a CMP process or the like is used for processing the surface of the divided recording elements and non-magnetic material, regions around the top face and side face of the divided recording elements are apt to be chemically and physically influenced by slurry or the like, and are often subjected to deterioration such as corrosion.
Further, such deterioration of the divided recording elements may occur with time after the processing.
Such deterioration of the divided recording elements may deteriorate the magnetic properties and hence decrease the recording/reading performance of the magnetic recording medium.
In other words, since magnetic recording media have peculiar problems such as their magnetic material being prone to oxidize and so on, it has been difficult to manufacture a discrete type magnetic recording media affording high recording/reading performance while reliably preventing the deterioration of divided recording elements, by directly applying a conventional processing method, that might be very effective in the field of semiconductor manufacturing.